Applications of Computational Fluid Dynamics Simulations in Urban Environments and Experiments Designed to Aid the Development and Evaluation of these Models
Progress in development of CFD models has shown their great potential for prediction of air flow, heat dissipation, and dispersion of air pollutants in the urban environment. Work at Lawrence Livermore National Laboratory has progressed using the finite element code FEM3 which has been ''massively parallelized'' to produce flow fields and pollutant dispersion in a grid encompassing many city blocks and with high resolution. While it may be argued that urban CFD models are not yet economical for emergency response applications, there are many applications in assessments and air quality management where CFD models are unrivaled in the level of detail that they provide. We have conducted field experiments to define the flow field and air tracer dispersion around buildings as a means of critiquing and evaluating the CFD models. The first experiment, the ''B170 study'', was a study of flow field, turbulence, and tracer dispersion in separation zones around a complex, single building. The second was the URBAN 2000 experiment in downtown Salt Lake City where flow fields and tracers were studied in nested resolution from the single building scale up to larger scales of 25 city blocks, and out to 6 km. For the future an URBAN 2003 experiment is being planned. We review the salient features of these experiments. A ''breakthrough'' technology in urban diffusion modeling is the use of modified computational fluid dynamics models (CFD) that use the meteorological conventions of large eddy simulation to represent the flow field. These CFD models have been initialized from the output of mesoscale atmospheric models with 4 km grid resolution, apparently with no problems although questions remain about aliasing and sources of bias. While more work remains, it is clear that should progress continue a remarkable tool should be available for such applications as: (1) Vulnerability studies for chemical, biological, and nuclear terrorism; (2) Assessments of air quality for urban pollutants--CO, NO, O{sub 3}, and particulates; (3) Preparing for disease outbreaks which are transmitted by wind; (4) Inhalation exposure attribution downwind of industrial releases; (5) Mitigation of susceptible populations of exposed individuals; (6) Mitigation of problems inside buildings through heating and ventilating intakes; and (7) Planning for emergency response where scenarios may be studied beforehand. Simulations and experiments in these complex cases have been made to interact. We have used rough case studies with CFD models to plan the experiment. That is, since measurement resources are limited they should be placed where we should get the most gain in developing or evaluating the models. Eventually the knowledge about the urban atmosphere is summarized and tested in the models. Of course, we have utilized wind tunnel or water channel data to evaluate the models as well. But the large scales of motion in the atmosphere and the complex urban heat island and turbulent wake mixing in real urban settings have made it necessary to have prototype experimental data. Urban meteorology or urban fluid mechanics is an evolving field (4) with many challenges to define the surface boundary layer and thermal influences. But the need is great with so many people living in the urban zones, and there will be an eventual demand for the weather forecasts to be made for specific land use zones (5).
- Research Organization:
- Lawrence Livermore National Lab. (LLNL), Livermore, CA (United States)
- Sponsoring Organization:
- US Department of Energy (US)
- DOE Contract Number:
- W-7405-ENG-48
- OSTI ID:
- 15005980
- Report Number(s):
- UCRL-JC-142263; TRN: US200402%%106
- Resource Relation:
- Conference: 2001 International Symposium on Environmental Hydraulics, Tempe, AZ (US), 12/05/2001--12/07/2001; Other Information: PBD: 22 Aug 2001
- Country of Publication:
- United States
- Language:
- English
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